1. Field of the Invention
The present invention relates to a liquid crystal display device (hereinafter, ref erred to as an LCD device) having wide viewing angle display characteristics, and a method for fabricating the same.
2. Description of the Related Art
Japanese Laid-Open Publication Nos. 6-301015 and 7-120728 disclose a technique of providing wide viewing angle characteristics for an LCD device. Such a technique includes steps of: dividing a liquid crystal layer into liquid crystal domains by surrounding regions thereof corresponding to pixels by a polymer wall; and aligning liquid crystal molecules in the respective liquid crystal domains in an axial symmetrical manner. Such a technique is called an axial symmetrically aligned microcell (ASM) technique. Using the ASM technique, an LCD device having a reduced change in contrast when the angle at which an observer views the LCD device changes in any direction (i.e., having wide viewing angle characteristics) is obtained.
In such an ASM mode, the control of the position of a symmetric axis (the axial position) is important. For example, as shown in FIG. 14, respective pixels have different axial positions 500a to 500f. When an observer views the LCD device while tilting the LCD device, the area of each pixel where the contrast changes and the area thereof where the contrast does not change vary depending on the pixels. As a result, the variation in the axial position among the pixels is observed as a difference in brightness among the pixels, thereby significantly reducing the display quality. This phenomenon is perceived by the observer as xe2x80x9croughnessxe2x80x9d of the screen.
Japanese Laid-Open Publication No. 8-292423 proposes a structure for overcoming the above problem, where concave portions or protrusions are formed for respective pixels for controlling the axial positions of the pixels. More specifically, an overcoat resin layer is formed on a colored layer, and a concave portion is formed on the overcoat resin layer. However, the publication does not disclose any concrete method for fabricating such a structure. The publication neither teaches nor suggests any other method for forming a concave portion other than a method for forming a concave portion on the overcoat resin layer.
Fujitsu Ltd. suggests a multi-domain vertical alignment (MVA) mode LCD device as another LCD device having wide viewing angle characteristics. The MVA mode utilizes a vertical alignment type liquid crystal cell and forms pyramid type protrusion structures on each of surfaces of a pair of glass substrates facing each other. The directions in which liquid crystal molecules fall are determined depending on respective tilted surfaces of the pyramid type protrusion structures. In other words, the directions in which liquid crystal molecules fall are not uniform over the liquid crystal cell, which enables the production of an LCD device having wide viewing angle characteristics. In the MVA mode, the protrusion structure is not necessarily disposed in the center of each pixel.
The above conventional method for fabricating the ASM mode LCD device includes several repetitions of a spin coat step and a photolithography step for forming concave portions in respective pixels. When a film is formed using the spin coat method, however, it is difficult to control the thickness of the film with high precision. Moreover, when a multilayer film is formed using the spin coat method, if a layer formed by a first spin coat step is uneven, a layer formed by a subsequent spin coat step is affected by the unevenness of the underlying layer. This further makes it difficult to control the thickness of the film with high precision. In addition, several repetition of the photolithography step (including resist application, light exposure, and development) increases the possibility of an occurrence of a factor which can reduce the yield, such as positional displacement and attachment of foreign matters. For the above reasons, in the conventional fabrication method, it is difficult to simplify the steps and suppress the production cost.
In the conventional method, a number of steps are required to form concave portions on a color filter layer substrate, thereby reducing the yield. Moreover, since colored layers constituting color filter layers are formed by the spin coat method, the thickness of the layers is not likely to be uniform, degrading the display characteristics of the color filter layers (Y value and chromaticity). In particular, when a thick layer is required, it is not possible to control the thickness over a wide area of the layer. Moreover, since an overcoat resin layer needs to be formed on each colored layer, such problems that the concave portions of respective pixels are not uniform and that the concave portions are buried within the overcoat resin, arise.
The liquid crystal display device of this invention includes a first substrate, a second substrate opposing the first substrate, and a liquid crystal layer sandwiched between the first and the second substrates, wherein the liquid crystal layer includes a polymer region and a liquid crystal domain surrounded by the polymer region in which liquid crystal molecules are oriented in an axial symmetrical manner, the first substrate includes a dry film having a concave portion on a surface facing the liquid crystal layer, and a symmetric axis in the liquid crystal domain substantially extends through the concave portion and is substantially perpendicular to the first substrate.
In one embodiment of the invention, the dry film is a colored film.
In another embodiment of the invention, the colored film is located on a colorless film having an opening.
In still another embodiment of the invention, the dry film is a colorless film, the colorless film has an opening, and the colorless film is located on a colored film.
In still another embodiment of the invention, the second substrate includes a channel portion in which a rare gas is enclosed and an anode electrode and a cathode electrode disposed inside the channel portion, and a potential difference is provided in the liquid crystal domain by applying a voltage between the anode electrode and the cathode electrode to generate plasma discharge in the channel portion.
Alternatively, the liquid crystal display device of this invention includes a first substrate, a second substrate opposing the first substrate, and a liquid crystal layer sandwiched between the first and the second substrates, wherein the liquid crystal layer includes a polymer region and a liquid crystal domain surrounded by the polymer region in which liquid crystal molecules are oriented in an axial symmetrical manner, the first substrate includes a transparent electrode having a concave portion on a surface facing the liquid crystal layer, and a symmetric axis in the liquid crystal domain substantially extends through the concave portion and is substantially perpendicular to the first substrate.
In another embodiment of the invention, the second substrate includes a channel portion in which a rare gas is enclosed and an anode electrode and a cathode electrode disposed inside the channel portion, and a potential difference is provided in the liquid crystal domain by applying a voltage between the anode electrode and the cathode electrode to generate plasma discharge in the channel portion.
According to another aspect of the invention, a method for fabricating a liquid crystal display device is provided. The method includes the steps of: forming a dry film on a first substrate; forming a concave portion on the dry film; arranging the first substrate to face a second substrate so that the concave portion of the dry film is located inside; injecting a precursor mixture of a polymerizable material and a liquid crystal material in a space between the first and second substrates; forming a polymer region and a liquid crystal domain surrounded by the polymer region in which liquid crystal molecules are oriented in an axial symmetrical manner by subjecting the precursor mixture to phase separation polymerization; and controlling the liquid crystal domain during the phase separation polymerization so that a symmetric axis in the liquid crystal domain substantially extends through the concave portion and is substantially perpendicular to the first substrate.
In one embodiment of the invention, the step of forming a concave portion on the dry film includes the step of partly removing a colored dry film in a thickness direction.
In another embodiment of the invention, the step of forming a concave portion on the dry film includes the steps of: forming a colorless dry film having an opening; and forming a colored dry film on the colorless dry film.
In still another embodiment of the invention, the step of forming a concave portion on the dry film includes the steps of: forming a colored dry film; forming a colorless dry film on the colored dry film; and forming an opening on the colorless dry film.
Alternatively, the method for fabricating a liquid crystal display device of this invention includes the steps of: forming a transparent electrode on a first substrate; forming a concave portion on the transparent electrode; arranging the first substrate to face a second substrate so that the concave portion of the transparent electrode is located inside; injecting a precursor mixture of a polymerizable material and a liquid crystal material in a space between the first and second substrates; forming a polymer region and a liquid crystal domain surrounded by the polymer region in which liquid crystal molecules are oriented in an axial symmetrical manner by subjecting the precursor mixture to phase separation polymerization; and controlling the liquid crystal domain during the phase separation polymerization so that a symmetric axis in the liquid crystal domain substantially extends through the concave portion and is substantially perpendicular to the first substrate.
Thus, according to the present invention, since a concave portion for each pixel region can be formed on a color filter layer, an increase in the number of steps can be minimized.
When the concave portion is formed on a colored layer which is to be a color filter layer, the concave portion of the colored layer tends to become thin. If the colored layer is not thick enough, the thickness of the concave portion is insufficient, causing decoloration. In order to prevent this problem, according to the present invention, the thickness of the colored layer is made larger by about 10% compared with a colored layer which has no concave portion.
By forming the color filter layer using a dry film resist, a uniform thickness is obtained over a wide area even if the color filter layer is thick. This enables the production of a color filter layer which is uniform in the Y value and chromaticity according to the CIE standard in the plane of the substrate. Moreover, since the concave portion in each pixel region is shallow according to the present invention, the display characteristics of the color filter layer are not degraded.
According to the fabrication method of the present invention, the concave portion in each pixel region may be formed on a colorless dry film. In this case, since the color filter layers for pixels of the same color have the same thickness, the display characteristics of the color filter layers are not degraded.
When the concave portion is formed on a colorless dry film formed on a colored layer, no processing is performed on the colored layer. Accordingly, the color characteristics and the brightness are not degraded.
When the concave portion is formed on a transparent electrode, the fabrication steps can be simplified if the present invention is applied to a large-scale liquid crystal display device which uses a thick transparent electrode.
Thus, the invention described herein makes possible the advantages of (1) providing an ASM mode liquid crystal display device capable of easily controlling the axial positions, and (2) providing a method for fabricating such a liquid crystal display device.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.